This invention relates to an improved cylinder head and more particularly to a cylinder head for a multiple valve internal combustion engine.
In internal combustion engines, it has been recognized that the breathing ability and performance of an engine can be significantly improved by utilizing multiple valves. For this reason, four valve per cylinder engines are commonly used. Such engines have two intake and two exhaust valves for each cylinder. Although the use of these engines was previously limited to high performance racing engines, many conventional passenger car engines now employ four valves per cylinder.
By utilizing more valves per cylinder rather than individual large valves, the effective flow area can be maintained while the inertia of the individual components reduced. This permits operation of the engine at higher speeds and the obtaining of higher power output.
It has also been recognized that further improvements in performance can be obtained by utilizing five valves per cylinder. Such five valve engines normally employ three intake valves and two exhaust valves per cylinder. However, the addition of the further intake valve give rise to problems which are not attendant with four valve per cylinder engines and which must be addressed.
With four valve per cylinder engines, the valves can be symmetrically positioned and all of the intake valves and all of the exhaust valves are operated by a respective cam shaft. Because of the symmetric positioning, the cylinder head fasteners can be assessable even when the camshafts are in place. In addition, relatively large tappet bodies may be employed for operating the valves without necessitating comprises in the cylinder head configuration to accommodate the various components.
Where, however, three intake valves per cylinder are employed the positioning of the valves is important. That is, it is relatively easy to add a third intake valve to the engine but doing so results in larger cylinder head surfaces forming the combustion chamber, large volumes, greater quenching and lower compression ratios.
Therefore, it has been proposed to position the three intake valves in such a manner that there is provided a center intake valve and a pair of side intake valves. The axes of reciprocation of the side intake valves lie in a common plane while that of the center intake valve is disposed at an angle to this plane. Conventionally and in order to obtain high compression ratios and low surface areas, it has been the practice to have the angle of the plane and the angle of reciprocation of the center intake valve at relatively shallow acute angles to a plane containing the cylinder bore axis. These acute angles also all lie on the same side of this plane. By appropriately positioning the valves, their valve stem axes may be disposed so that they all can be operated by a common intake camshaft through thimble tappets.
Although this result is obtainable, it generally results in the positioning of the intake camshaft in such a location that it overlies or obscure the axis and heads of the cylinder head fasteners. Obviously, this presents some difficulties from a service standpoint.
Also, when three intake valves are utilized and they are all actuated by thimble tappets, then the thimble tappets must be relatively small in diameter to avoid interference. This can increase unit stress and wear.
It is, therefore, a principal object to this invention to provide an improved cylinder head arrangement for internal combustion engine employing multiply and at least three intake valves per cylinder.
It is a further object to this invention to provide a cylinder head assembly for such a multiple valve engine wherein the valves are positioned in such a way so as to maintain low surface areas and high compression ratios.
It is a further object to this invention to provide a cylinder head arrangement for such an engine wherein the camshafts may be positioned so that only two camshafts are required for operating all five valves and so that the camshafts are positioned so that they do not obscure the cylinder head fasteners.
It is a still further object to this invention to provide a multi-valve cylinder head arrangement wherein the diameters of the respective valve actuating tappets may be maintained as large as possible without interference between them.